This invention relates to rotor blades and specifically to the mechanical damping of vibratory energy in the blades of rotor assemblies during operation. Rotor assemblies are used in a variety of turbo-machines, such as turbines and compressors. During operation, fluid forces induce vibratory stresses on the blades, resulting in high cycle fatigue and potential failure of the blades. Dampers, commonly frictional dampers, are utilized to reduce the magnitude of these dynamic stresses, thereby increasing operational life of the blades.
Typically the most effective frictional dampers are located on the turbine blade shroud. The shroud is located at the radial tip of the rotor blade adjacent the stationary housing. During operation, centrifugal forces urge the damper into frictional contact with its adjacent blade shroud. This contact reduces the relative motion between the adjacent blades, thereby reducing the vibratory stresses on the blades during operation. Frictional damping is effective so long as relative motion exists between the damper and the blade. When the rotor speed becomes high, typical flat plate shroud dampers become too heavy and the frictional damper sticks to the shroud due to friction thereby reducing its effectiveness. Typical lighter weight damper designs consist of loss fitting rivets. These rivets are hard to form due to the many tight tolerance features required and they are exposed to the main gas flow.
Other efforts to reduce vibrational damage not only are structurally deficient in affecting the clearances of the shroud, they are subject to fatigue that further reduces their effectiveness.
Conventional shrouds typically include one or more sealing rails that extend radially outward from the shroud in close proximity to the stationary housing and typically extend continuously across the top surface of the shroud between first and second circumferential sides. Typical previous shroud frictional dampers are retained by extra features added to the shroud. These added features are located on the shroud at the furthest distance from blade which increases the shroud overhung weight. These added features increase the centrifugal induced bending stress in the shroud which may result in potential failure of the rotor assembly due to high cycle fatigue. To counteract this, the shroud thickness must be increased. This increase in shroud thickness also results in higher centrifugal stress in the blade at the blade's two critical locations, the blade shank and firtree.
What is needed is a way to place any damper out of the main gas flow of turbo-machines without adversely affecting the function of the shroud.